Electric valve commutation circuits



July 25, 1950 ELECTRIC VALVE C A. SCHMIDT, JR

OMMUTATION CIRCUITS Filed Sept. 9, 1949 Fig.3.

EXCHTATI ON AND CONTROL C\RCUIT$ hnvehtor: August Schvmdt JTT,

His Att ovney.

Patented July 25, 1950 ELECTRIC JVALVECOMM'UTATION omoorrs AugustSchmidt, Jr., Schenectady, N. Y., assignor to GcneralElectric Company, acorporationof New York Applicationseptember 9, 1949, Serial 'No.114,7=50

My invention relates to electric valve commutation circuits for electricdischarge devices or electric valve means of the type employingi'onizable mediums, such as gases or vapors.

In electric valve circuits such as-multiple phase electric valverectifying circuits, theproblem of preventing arc-back is consistentlypresent. One of the precautionary measures in preventing arcback is toassure positive commutation between conduction of the current throughone valve to conduction throughanother valve. This may be accomplishedby assuring the early decay of the .current'in each valve just before itis tostop conducting. More specifically, diminution of arcback frequencymay be achieved by slowing downa the rate .of decay of anode currentwhen. the anode current approaches zero, so that a low value of anodecurrent-will be maintained for an appreciable time before initialinverse voltage is applied to the anode. During this time the highionization density associated with normal load current will have anopportunityto difiuse and the reduced ion density at the time inversevoltage is first applied will result in :areduced prob ability ofarc-back.

It is, therefore, an object of my invention to provide an electric valvetranslating apparatus including an improved means for assuring the earlydecay of the current in each electric valve immediately preceding itsnon-conductive period. My invention consists essentially in an electricvalve circuit employing auxiliary reactors connected with the electricvalve apparatus supply transformer primary windings to obtain voltagesat the electric valves which, because of their wave shape, assure ggoodcommutation.

For a better understanding of my invention, reference may be had to thefollowing description taken in connection with the-accompanyingdrawings, and its .scope will be pointed out in the appended claims. Inthe 'drawingsl ig. .1 shows an embodiment of my invention wherein theelectric valve supply transformer primary is connected in delta, and inFig. 2 is shown a second embodiment of my invention wherein the electricvalve supply transformer primary is connected in Y.

Referring now to the accompanying drawing, my invention is thereillustrated as applied to a polyphase rectifying or translating systemfor energizing a direct current load circuit including a positiveconductor l and a negative conductor 2, from an alternating currentsupply circuit 3. The electric translating apparatus also comprises aninductive network including a plurality 3 Claims. (Cl. 321-11) ofelectrically displaced windings which may be provided by a transformer4, including primary windings 5, 6, and 1 and secondary windings 8, 9,1-D, and :l I, l2, l3.

To each of the secondary windings is connected an electric valve means15, preferably of the type employing anionizable medium such as a gas ora vapor, and includingan-anode 't6, a cathode l'l,

and'a control member 18, such as an immersionig-niter typecontrolmember-constructed of a material such as'boron carbide or siliconcarbide,

andwhichhas an electrical resistivity relatively ia-rgc compared withthat of the mercury of the associated pool cathode. The electric valveControl member i8 is :connected through cur- .rent limiting andstabilizing resistance 23 and unidirectional conducting :device 2| tothe excitation and control circuits which are indicated generally at 22.These excitation and control circuits arenot-shownindetail here, sincethey form no part of my invention. Any suitable control and excitationcircuit may be used such, for instance, :as that disclosed in Patent2,362,294, issued on November -7, 1944, to A. I-LMittag, and assigned tothe same assignee as the present application. Relieving electrode I9 isalso connected to theexcitation-and control circuits through a currentlimiting reactor 23.

Connected with transformer primary windings 5, 6,, and .l arecummutating reactors 24, 25, and .26. Each of these commutating reactorsincludes a main coil section 2] and a pie-saturating coil section 28. twill be-seen in Fig. 1 that the main coil sections of the commutatingreactors are respectively connectedin series with the associated primarywindings .in a primary winding delta configuration, while the:pre-saturating sections 2.8 are connected respectively in series withthe supplylines from the supply circuit 3 to the delta. The current inthe pie-saturating section is, therefore, line current, while thecurrentin the remainder of the commutating reactor and transformerwinding is delta current; thus, there is approximately a 30 degree phasedisplacement between the current in the presaturating section and thecurrent in the main coil section of the commutating reactor.

Commutating reactors 24, 25, and 26 are of the saturable type and aresaturated when the apparatus is conducting an appreciable value of loadcurrent but have substantially their full unsatupreceding higher valuesofanode current and, I

thus, reduces the probability of arc-backs when inverse voltage isapplied.

In order for the commutating reactors 24, 25, and 26 to be completelyoperative as above described, they must reach their unsaturatedcondition in each half cycle for an appreciable period before theoccurrence of the current zero in their respective associatedtransformer secondary windings 9l3 in order that the current may bereduced for valve deionization. Normally, this would not occur becauseof the phase lag due to the magnetic hysteresis efiect in the cores ofthese reactors. I, therefore, provide what I call a pre-saturating coilsection in each of these commutating reactors which, in the embodimentof Fig. 1, are connected in series with the power supply lines to thedelta configuration of the transformer primary windings 5, 6, and 1.Thus, each of these pre-saturating sections 28 carry line current, whichhas a slight phase ad- Vance over the current in the associated primarywinding and main coil section. Thus, the combined magnetic'result of thecurrent in the main coil section and the currentin the pre-saturatingcoil section of each of my commutating reactors is to advance the phaseof the saturated and unsaturated conditions of the commutating reactorswith relation to the current in the associated secondarywindings, thuscorrecting for the undesirable lag due to hysteresis effect, asmentioned above. The current in each valve is thus reduced toarelatively small value for an appreciable period in eachhalf cycle ofvalve conduction immediatelypr-ior to commutation.

. This period of low current permits the valve to partially de-ionize,which'reduces thepossibility of arc-back to a minimum. I

In Fig. 2 is shown an alternative embodiment of my invention wherein thetransformer primary windings and the main coil sections of thecommutating reactors are connected in a Y configuration and theassociated pre-saturating coil sections 28 are connected in-delta at thecenter of the Y. The remainder of the system for Fig. 2 is similar tothat'shown for Fig. 1-.

It will, therefore, be seen from the above description and disclosurethat I have provided an extremely simple and economical means forimproving commutation in electric valve translating apparatus which isparticularly characterized by comparatively low first cost and ease ofmaintenance. i I

While I have shown and described my invention as applied to a particularsystem of connections and as embodying various devices diagrammaticallyshown, it will be obvious to those skilled in the art that changes andmodifications may be made without departing from my invention and I,therefore, aim in the appended claims to cover all uch changes andmodifications as fall within the true spirit and Scope of my invention.

:What I claim as new and desire to secure by Letters Patent of theUnited States is; 1. In combination, a multiple-phase supply circuit, aload circuit, electric translating apparatus connected between saidcircuits and including a plurality of electric valve means andmultiple-phase inductive apparatus having primary windings and secondarywindings connected tosaid valve means, a commutating reactor for each ofsaid primary windings having a main coil section connected in serieswith the associated primary winding and a pre-saturating coil sectionconnected to conduct a part of the current from another of said primarywindings and thereby to conduct a total current having a phasedisplacement from the current to be conducted in the associated maincoil section and primary winding.

2. In combination, a multiple-phase supply circuit, a load circuit,electric translating apparatus connected between said circuits andincluding a plurality of electric valve means and multiple-phaseinductive apparatus having primary windings and secondary windingsconnected to said valve means, a commutating reactor for each of saidprimary windings having a main coil section connected in series with theassociated primary winding, said primary windings and associated maincoil sections being recurrent having a phase displacement from the deltacurrent to be conducted in the associated main coil section and primarywinding.

-ings and associated main coil sections being respectively connected ina Y configuration, said commutating reactors including pre-saturatingcoil sections respectively connected in delta at' I the center of said Yconfiguration and thereby adapted to carry a line current having a phasedisplacement from the delta current to be conducted in the associatedmain coil section and primary winding.

AUGUST SCHMIDT, JR.

No references cited.

